1. Field of the Invention
The present invention is related to a network apparatus and communication device, and more particularly, to a network apparatus and communication device capable of grouping aggregated component carriers.
2. Description of the Prior Art
Carrier aggregation (CA) is first introduced in long-term evolution advanced (LTE-Advanced or 3GPP Release 10) standard in order to increase the bandwidth and thereby increase the bitrate. Each aggregated carrier is referred as a component carrier (CC). The CC can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz and a maximum of five CCs can be aggregated, hence the maximum aggregated bandwidth is 100 MHz.
The CA can be used for both frequency division duplexing (FDD) LTE and time division duplexing (TDD) LTE systems. In the FDD LTE system, a number of CCs can be different in downlink (DL) and uplink (UL). However, the number of UL CCs is always equal to or less than the number of DL CCs. Notably, the individual CCs can also be of different bandwidths.
In order to be compatible with previous LTE standards, such as 3GPP Release 8 and 3GPP Release 9, the CA is arranged to use contiguous CCs within a same operating frequency band, so-called intra-band contiguous CA. However, such an arrangement might not be always possible due to practical operator frequency allocation limits. On the other hand, non-contiguous CCs allocation might be either an intra-band, i.e. the CCs belong to a same operating frequency band having a gap or gaps between the CCs, or an inter-band in which the CCs belong to different operating frequency bands.
The CA of the 3GPP Release 10 enables aggregation of up to 5 carriers of the same frame structure. Extensions of the basic carrier aggregation framework nowadays enable inter-band TDD CA with different UL-DL configurations, CA with multiple UL timing advance (in 3GPP Release 11), and aggregation of carriers with different frame structures through FDD-TDD CA (in 3GPP Release 12). To more efficiently utilize the available spectrum for communication requirements, extension of the CA framework beyond 5 carriers to 32 CCs is considered and discussed in 3GPP Release 13.
However, not all the CA aspects scale directly with an increasing number of CCs. For example, if the number of CA capable user equipments (UEs) and (or) the aggregated CCs increase, a cell used as the primary cell (PCell) will be highly loaded because there are key features which are only applied to the PCell, i.e. a feedback of an uplink control information (UCI) in a physical uplink control channel (PUCCH). The increase of the number of supported CCs results in an even greater increase for the required PUCCH payload size per CA UE, which leads to a severe impact on PCell UL load with increasing number of CA UEs. Accommodating all the PUCCH transmissions in the PCell apparently impacts performance, especially for the non-CA UEs. Therefore, the requirement to accommodate all the PUCCH transmissions in the PCell hinders the development to future CA enhancement. Also, the mechanism for UL power control does not scale with the increasing CCs.
Therefore, the LTE system has to be further developed to deal with the increase of the supported CCs.